1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor, and particularly relates to a multilayer ceramic capacitor ready for a small size and large capacity.
2. Description of the Related Art
A multilayer ceramic capacitor as an example of electronic devices is produced, for example, by printing a predetermined pattern of internal electrodes on a ceramic green sheet made by a predetermined dielectric ceramic composition, stacking a plurality of the results, then unifying the same, and cofiring a thus obtained green chip. It is necessary that a material which does not react with a ceramic dielectric has to be selected for the internal electrode layer of the multilayer ceramic capacitor so as to be unified with the ceramic dielectric by firing. Therefore, costly precious metals, such as platinum and palladium, had to be used as the material composing the internal electrode layer.
However, in recent years, a dielectric ceramic composition wherein an inexpensive base metal, such as nickel and copper, can be used has been developed and a major cost reduction has been realized.
Also in recent years, a demand for a more compact electronic device has become high along with an electronic circuit becoming high-density, and a multilayer ceramic capacitor has been rapidly becoming more compact and higher in capacity. To respond to the demand, there has been used a method of making a thickness of one dielectric layer thinner in a multilayer ceramic capacitor.
However, when a dielectric layer is made thinner, there arises a disadvantage that a short-circuiting defective of a multilayer ceramic capacitor is frequently caused. To solve the disadvantage, there is a method of making dielectric particles finer. However, when dielectric particles are made finer, the permittivity largely declines. Accordingly, it has been considered to be difficult to suppress short-circuiting defectives and obtain a high permittivity when dielectric layers are made thinner.
As a method of solving the above disadvantages, the Japanese Unexamined Patent Publication No. 2001-316114 discloses a method below. According to the article, the above disadvantages are solved by making a particle diameter of an oxide having the perovskite structure, such as barium titanate, to 0.03 to 0.2 μm.
However, in the invention disclosed in the article, particularly in the invention disclosed in the examples, fine barium titanate raw powder is used, and when such barium titanate raw powder is used, additional subcomponent materials are hard to be dispersed when producing a dielectric paste, so that the subcomponent materials have to be easily dispersible. Furthermore, in the examples of the article, a relatively large quantity of Mg is contained as a subcomponent. Since Mg generally has a function of suppressing a peak of a permittivity at the Curies point of barium titanate, an increase of the adding quantity of Mg may lead to a problem in the temperature characteristic, particularly the temperature characteristics on the high temperature side.
Also, the Japanese Unexamined Patent Publication No. 9-35985 discloses a ceramic multilayer electronic device wherein the ceramic particle number “n” (note that the ceramic particle number “n” is “thickness of the ceramic layer”/“average particle diameter of the ceramic particles”) existing along the thickness direction of a ceramic layer positioned between internal electrodes is made to be less than 5. The article describes that, by configuring the ceramic multilayer electronic device as above, the delamination phenomenon, cracks and other structural defectives can be effectively prevented.
However, the ceramic multilayer electronic device, particularly the ceramic multilayer electronic device disclosed in the examples disclosed in the above Japanese Unexamined Patent Publication No. 9-35985 only refers to structural defectives, such as delamination and cracks and electric characteristics thereof are unknown. Furthermore, a thickness of a ceramic layer of the ceramic multilayer electronic device described in the examples is 5 μm, and the multilayer ceramic capacitor is hard to be compact and high in capacity with the thickness. Accordingly, in the article, when the dielectric layer (ceramic layer) is made thinner (for example, to 2.0 μm or less), a range of the particle number in the thickness direction in the dielectric layer to obtain a multilayer ceramic capacitor having preferable characteristics (for example, electric characteristics) is not known.